Thermally-activated shape memory alloys for retrofitting bridge double-angle connections

Mohammadreza Izadi,Masoud Motavalli,Elyas Ghafoori

doi:10.1016/j.engstruct.2021.112827

Abstract

Double-angle connections are prone to fatigue cracking in old steel bridges; however, owing to their complexity, there are not many retrofitting solutions for these details. This study proposes a retrofitting system for double-angle connections using iron-based shape memory alloys (Fe-SMAs). An innovative connection test setup equipped with an optical 3D digital image correlation (DIC) measurement system was developed. The retrofitting system included two end-anchorages set on either side of the connection. Fe-SMA strips were inserted inside the anchorages, and then were thermally activated (pre-stressed) to a temperature of 260 °C. Numerical finite element studies were performed to investigate the static behavior of the system. It was found that the activated/prestressed Fe-SMA strips not only apply a reverse positive moment on the connection (versus an undesirable negative fixity moment), but also “absorb” a portion of the negative moment, owing to the added axial stiffness. The proposed SMA-based system offers a versatile and cost-effective technique (with quick and easy installation) for bridge connections, and can significantly reduce the effects from undesirable sources of fatigue cracking.

Highlights

The fatigue cracking of in-service steel bridges is a major problem regarding the serviceability of aged highways and railway bridges
Al-Emrani [3,4,13,14] determined that the flexural stiffness of the outstanding leg mainly affects the flexural stiffness of the connection
The displacement contours resulting from the digital image correlation (DIC) measurements agree well with the Finite element (FE) modeling results

Summary

Introduction

The fatigue cracking of in-service steel bridges is a major problem regarding the serviceability of aged highways and railway bridges. Among the categorized fatigue-prone details, the connections be tween the longitudinal and transversal beams (so-called stringers and crossbeams, respectively) are reported as the most prevalent. As discussed in several studies regarding fatigue evaluations of stringer-to-floor beam double-angle connections [1,4,6,7], a restraining moment is induced on the stringer end from the connection. This unpredicted semi-rigidity of the doubleangle connection explains the secondary effect of this type of fatigueprone detail. This resulted in the formula proposed by Wilson [14,15] for guaranteeing the sufficient flexibility of the outstanding leg, so as to reduce the rigidity of the connection

Methods

Results

Discussion

Conclusion